1. Technical Field
The present invention relates to a liquid crystal device and, more particularly, to a technology suitably applied to a liquid crystal device, typically, a so-called fringe field switching (hereinafter, referred to as FFS) mode liquid crystal device, in which both pixel electrodes and a common electrode are provided in an element substrate. In addition, the invention also relates to a method of manufacturing the liquid crystal device and to an electronic apparatus to which the liquid crystal device is applied.
2. Related Art
Among various liquid crystal devices, an FFS mode liquid crystal device is configured so that, between an element substrate and an opposite substrate, pixel electrodes, an interelectrode insulating film and a common electrode having openings formed therein are laminated in the element substrate, and liquid crystal is driven through an electric field applied between the pixel electrodes and the common electrode, which is described in Japanese Unexamined Patent Application Publication No. 2001-235763.
In the above FFS mode liquid crystal device, when bottom-gate thin-film transistors, which employ an amorphous silicon film, are used as pixel switching elements, and pixel electrodes are formed so as to directly overlap the drain electrodes of the thin-film transistors, the pixel electrodes are formed in the interlayer in which data lines are formed. Therefore, it is necessary to space the pixel electrodes apart from the data lines and, hence, there is a problem that an area for forming the pixel electrodes is small.
Then, it has been proposed that, as shown in FIG. 7A, an interlayer insulating film 6 is formed so as to cover a thin-film transistor 30, which serves as a pixel switching element, and a pixel electrode 7a is electrically connected through a contact hole 6a of the interlayer insulating film 6 and a drain electrode 5b to a drain region 1d of the thin-film transistor 30. An example shown in FIG. 7A is provided in order to make comparison with the aspects of the invention. In the example, in the upper side layer of the pixel electrode 7a, an interelectrode insulating film 8, a common electrode 9a in which slit-like openings 9b are formed, and an alignment layer 16 are sequentially formed. The pixel electrode 7a and the common electrode 9a both are formed of ITO (indium tin oxide) films having the same thickness of 100 nm to 200 nm. With this configuration, the pixel electrode 7a may be formed up to a position in proximity to a data line 5a, and it is advantageous in that the area for forming the pixel electrode 7a may be increased.
When a liquid crystal device is manufactured using the above configured element substrate 10, as shown in FIG. 7B, after the alignment layer 16 formed of polyimide resin is formed on the surface side of the common electrode 9a, a rubbing process, in which the surface of the alignment layer 16 is rubbed by using a rubbing roller 40, or the like, is performed. Thus, the alignment of liquid crystal molecules in a state where no electric field is applied is controlled. In order to perform the rubbing process uniformly over the entire surface of the alignment layer 16, the surface of the alignment layer 16 is preferably even, so that an organic planarizing film is preferably used for the interlayer insulating film 6.
However, when the rubbing process is performed in the configuration shown in FIG. 7A and FIG. 7B, in a direction in which the rubbing roller travels relative to the common electrode 9a, rubbing defects 16a problematically occur inside the openings 9b of the common electrode 9a over a wide area because of large steps due to the thickness of the common electrode 9a. The rubbing defects 16a cause a decrease in quality of display image, such as a decrease in contrast. On the other hand, when the thickness of the common electrode 9 and the thickness of the pixel electrode 7a are reduced, the electrical resistance of the common electrode 9a is increased. The increase in the electrical resistance causes generation of luminance non-uniformity, or the like, in an image.
In addition to the above rubbing defects, when the thickness of the common electrode 9a is large, there is a possibility that alignment defect occurs due to steps themselves or the contrast of display decreases due to variation in thickness of a liquid crystal layer in a pixel between an area in which the common electrode 9a is formed and the slit-like openings 9b. 
The above problems not only occur when the common electrode 9a is formed on the interelectrode insulating film 8 but also occur when the pixel electrodes 7a are formed on the interelectrode insulating film 8.